th - 1988 - 51st ENC Conference
th - 1988 - 51st ENC Conference
th - 1988 - 51st ENC Conference
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[WED 11:45 ] ANGIOGRAPHY USING MAGNETIC RESONANCE, Albert<br />
Nishimura, Dept. of EE, Stanford University, Stanford CA 94305<br />
Macovski~ and Dwight G<br />
Vessel disease is <strong>th</strong>e number one killer of western man, wi<strong>th</strong> coronary artery lesions<br />
<strong>th</strong>e principal source of heart disease, and carotid artery lesions <strong>th</strong>e principal source<br />
of strokes. We will present an array of techniques for studying <strong>th</strong>ese vessels wi<strong>th</strong><br />
magnetic resonance imaging, a completely non-invasive procedure. Each of <strong>th</strong>e approaches<br />
involves one or more combinations of <strong>th</strong>ree basic techniques: Phase shift in <strong>th</strong>e pres-<br />
ence of a gradient, wash-in wash-out effects, or cancellation excitation. The first is<br />
a classical phenomenon whereby moving material acquires a phase shift proportional to<br />
<strong>th</strong>e velocity component in <strong>th</strong>e gradient direction. Systems have been developed which<br />
subtract <strong>th</strong>e signals from two sequences having differing first gradient moments, <strong>th</strong>us<br />
displaying solely <strong>th</strong>e moving material. The second approach involves an upstream excita-<br />
tion followed by a downstream readout, or a variety of similar approaches. We have been<br />
~articularly successful wi<strong>th</strong> an approach where <strong>th</strong>e source of blood is subjected to an<br />
Lnversion excitation on one sequence and left unexcited on <strong>th</strong>e next. When <strong>th</strong>ese are<br />
subtracted, using identical readout sequences, all static tissue cancels while <strong>th</strong>e<br />
vessels are clearly visualized due to <strong>th</strong>e large difference between <strong>th</strong>e inverted and<br />
fresh spins. The <strong>th</strong>ird approach involves excitations which provide a net excitation for<br />
moving material only, while statlc material is left unexcited using a form of driven<br />
equilibrium. These vessel images are structured as projections <strong>th</strong>rough <strong>th</strong>e volume of<br />
interest so <strong>th</strong>at <strong>th</strong>e entire vessel is visualized despite its tortuous pa<strong>th</strong>. One of<br />
<strong>th</strong>e major problems is <strong>th</strong>e phase shift produced by higher order moments, such as accel-<br />
eration due to turbulence. This can cause loss of signal in regions of narrowing, often<br />
I crucial portion of <strong>th</strong>e image. Imaging sequences can be designed to make <strong>th</strong>e readout<br />
ery close to <strong>th</strong>e excitation, minimizing <strong>th</strong>is problem.<br />
I<br />
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